It has been suggested to provide heating features in tools for forming plastic materials. The heating may be provided by inductive heating, i.e. by means of a coil that is provided with a high-frequency AC pulse. This may be used in injection moulding as well as in embossing/pressing of a plastic blank. The coil generates an oscillating magnetic field that, by inducing eddy currents, heats the mould or tool in the vicinity of the surface that will face the plastic material to be reshaped.
Cooling may also be provided by means of a fluid such as water, which flows in the vicinity of the tool or mould surface.
Different ways to achieve such heating have been disclosed. In US-2009/0068306-A a structure is shown having a coil carrier part which provides a magnetic field. The coil carrier functions as a soft ferrite and includes mutually electrically insulated magnetic granules, such as in PERMEDYN MF1. Closer to the mould or tool surface there is a top part for instance in the form of an austenitic steel which is not particularly ferromagnetic, and has a resistivity that is suitable, e.g. about 7*10−7 Ωm, to develop heat from eddy currents induced by the coil. On the other side of the coil carrier as seen from the top part there is a back plate, for instance made of copper, that has a considerably lower resistivity than the top part. The back plate short-circuits the induced eddy currents on the backside of the coil. On top of the top part there is a stamper that includes the pattern to be replicated on the resin or blank in the mould or tool. This stack of materials has cooling ducts close to the top part.
In US-2009/0239023-A a further developed structure is shown where the above-described stack of materials is provided with one additional layer that separates the coil carrier part from the top part. This intermediate layer may consist of a ceramic material which is more or less magnetically and electrically passive, but has high mechanical resistance. The cooling ducts may be placed in this intermediate layer. The high mechanical resistance of the intermediate layer implies that the top part can be thin and thus have a lower specific heat. Thereby, the cycles can be shorter as the top part can quickly be cooled and heated. Moreover, as the cooling ducts can be moved out of contact with the top part, higher temperatures can be used without boiling the water in the ducts.
One problem associated with the known art is how to further improve the efficiency of a process involving such tools, and to do this in a cost-efficient manner.